1. Field of the Invention
The present invention relates to flat panel displays generally, and more particularly, to an organic light-emitting display (OLED) device and method of fabricating the same, which improves contrast by independently forming a light-blocking layer on an entire surface between a thin film transistor (TFT) and an electrode (EL) element.
2. Description of the Related Art
FIG. 1A is a top view of a portion 100 of a conventional active-matrix organic light emitting display device (AMOLED), illustrating red (R), green (G) and blue (B) unit pixels. FIG. 1B is a top view of a unit pixel 140 used in a portion 100 of the conventional AMOLED shown in FIG. 1A.
In order not to unnecessarily complicate FIG. 1A, reference numerals applicable to each of the R, G, B unit pixels are indicated on only the R unit pixel. However, it will be appreciated that the R, G, B unit pixels are identically configured.
Referring to FIGS. 1A and 1B, a conventional AMOLED illustrated thereby, includes a plurality of gate lines 110 insulated from each other and arranged in one direction; a plurality of data lines 120 insulated from each other and arranged in a direction crossing the gate lines 110; a plurality of power lines 130 insulated from each other, crossing the gate lines 110 and arranged in parallel with the data lines 120; a plurality of pixel portions 140 formed within an area enclosed by the gate lines 110, the data lines 120 and the power lines 130; and a plurality of pixel electrodes 150 arranged in each of the pixel portions 140 and having openings 155.
R, G and B unit pixels are arranged in each of the pixel portions 140, and each unit pixel includes two transistors 160 and 180, a capacitor 170 and an EL element having a pixel electrode 150. Also, there is provided a via hole 189 for connecting the pixel electrode 150 with a drain electrode 185 of the driving transistor 180.
The switching transistor 160 includes a semiconductor layer 161 having source/drain regions (not shown in the drawings), a gate electrode 163 connected to the gate line 110, and source electrode 167 and drain electrode 165 respectively connected to the source/drain regions of the semiconductor layer through contact holes 164 and 166. Also, there is provided a via hole for connecting the TFT 160 with drain electrode 165. The driving transistor 180 includes a semiconductor layer 181 having source/drain regions (not shown in the drawings), a gate electrode 183, source electrode 187, and drain electrode 185 respectively connected to the source/drain regions of the semiconductor layer 181 through contact holes 184 and 186.
The capacitor 170 includes a lower electrode 171 and an upper electrode 173. The lower electrode 171 is connected to the drain electrode 165 of the switching transistor 160 through a contact hole 166, and connected to gate electrode 183 of the driving transistor 180. The upper electrode 173 is connected to the power line 130 to which the source 187 of the driving transistor 180 is also connected. The pixel electrode 150 is connected to the drain electrode 185 of the driving transistor 180 through the via hole 189.
FIG. 2 is a cross-sectional view of portions of a conventional organic light-emitting OLED device that correspond to the driving transistor 180, the pixel electrode 150 and the capacitor 170 shown in FIG. 1B.
Referring to FIG. 2, a buffer layer 210 is formed on an insulating substrate 200, and a semiconductor layer 220 having source/drain regions 221 and 225 is formed on the buffer layer 210. A gate electrode 231 and a lower electrode 237 of a capacitor are formed on a gate insulating layer 230. Source/drain electrodes 251 and 255 are connected to the source/drain regions 221 and 225 through contact holes (not shown), and an upper electrode 257 of the capacitor is connected to each of the source/drain electrodes 251 and 255. In this example, upper electrode 257 is connected to the source electrode 251 formed on an interlayer insulating layer 240.
A passivation layer 260 and a planarization layer 265 are formed on an entire surface of the substrate. A lower electrode 270 (e.g., a pixel electrode) of an EL element is connected to one of the source/drain electrodes 251 and 255. In this example, lower electrode 270 is connected to the drain electrode 255 through a via hole 269 formed on the planarization layer 265. A pixel defining layer 275 has an opening 279 to expose a portion of the lower electrode 270. An organic emission layer 280 is formed in opening 279 and contacts lower electrode 270. An upper electrode 285 is formed on the entire surface of the substrate.
A conventional organic light-emitting OLED device having a structure as described above typically uses a poly-silicon film TFT, and suffers decreased contrast when the EL element emits light. This reduction in contrast is caused by reflection of light off of a metal material within the OLED, such as a transistor, a capacitor, a wire, etc. In the case of mobile displays in particular, which are extensively exposed to exterior light, this is a serious problem because the contrast is drastically decreased by the internal reflections of the exterior light.
In order to prevent reduction of contrast due to the reflection of exterior light, an expensive polarizer is typically attached to a front surface of the display device. This leads to other problems in that addition of the expensive polarizer increases production costs. Moreover, the polarizer itself shields light emitted from the organic emission layer so that transmissivity is decreased, resulting in drastically reduced luminance.
Another conventional method forms a black matrix, composed of chromium (Cr)/chromium oxide (CrOx), or an organic layer, etc. on an area in which a TFT and a capacitor are formed. A significant disadvantage to this method is that a separate masking process is required to form the black matrix, resulting in a complex manufacturing process.
Where AMOLED devices are concerned, a method of forming the black matrix using a method that transforms the transmissivity of a transparent conductive layer was disclosed in Korean Patent Application Nos. 2002-0005435 and 2001-0075075. Although the techniques disclosed therein improved contrast and reduced the reflection of exterior light in bottom-emitting AMOLED devices, the problem caused by the reflection of the exterior light could not be solved in top-emitting AMOLED devices. Also, a metal layer used as a source or drain electrode, which forms an upper electrode of a capacitor, is highly reflective, and readily reflects exterior light.
In another case a black matrix was formed using a metal insulator hybrid layer (MIHL) in a top-emitting AMOLED but, because of a metal material in the MIHL, the black matrix had to be formed separately between pixels. Significant disadvantages of this method are that the black matrix does not completely shield the exterior light, and that an additional masking process is required to separate the black matrix between the pixels.